AutoIt

Large Persistent Hash Table Stored on Filesystem

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Demonstrates how to implement a large, persistent hash table that is stored on the filesystem and allows for quick retrieval using a hash key. AutoIt

Local $bSuccess = False

;  Let's say we would like to implement a persistent hash table with approximately 200,000 entries.
;  We want something simple and straightforward.
;  
;  The Chilkat Cache class is a solution that might fit.
;  
;  Each hash table entry is a file.  Depending on the number of anticipated hash entries,
;  the files can be contained in a single directory, or a collection of 256 directories,
;  or a collection of 256x256 directories.

;  There are 3 options:
;  
;  Level 0: All cache files are in a single directory (the cache root).
;  Level 1: Cache files are located in 256 sub-directories numbered 0 .. 255 directly under the cache root.
;  Level 2: There are two levels of sub-directories under the cache root. 
;           The 1st level has 256 sub-directories numbered 0 .. 255 directly under the cache root. 
;           The 2nd level allows for up to 256 sub-directories (0..255) under each level-1 directory. 
;           Cache files are stored in the leaf directories. 

;  For this example, given that we anticipate a larger number of hash entries, we choose a "level 2" cache.
$oCache = ObjCreate("Chilkat.Cache")

;  We can also spread the cache among several root directories, but for this example we'll only use one root directory.
;  Call AddRoot once for each root directory.
$oCache.AddRoot "c:/temp/myCache"
$oCache.Level = 2

;  Add some key/values to the persisted hash table (i.e. the cache).
;  The eTag is optional metadata.
Local $sKey = "apple"
Local $sETag = ""
Local $sItemValue = "macos"
$bSuccess = $oCache.SaveTextNoExpire($sKey,$sETag,$sItemValue)

;  Add more items..
$bSuccess = $oCache.SaveTextNoExpire("microsoft","","windows")
$bSuccess = $oCache.SaveTextNoExpire("google","","android")

;  Lookup items:
$sKey = "microsoft"
$sItemValue = $oCache.FetchText($sKey)
ConsoleWrite($sKey & ": " & $sItemValue & @CRLF)

$sKey = "apple"
$sItemValue = $oCache.FetchText($sKey)
ConsoleWrite($sKey & ": " & $sItemValue & @CRLF)